The skin itself is made of two layers, the epidermis made stratified squamous epithelium, and the dermis made of areolar and dense irregular connective tissue. The epidermis is keratinized in the body's external skin to help protect from abrasion and water loss and non-keratinized in the internal skin (the linings of the mouth, esophagus, anus, and vagina). In all locations the epidermis is continually replaced by mitosis at its base and exfoliation from its surface. Beneath the skin proper is the hypodermis or subcutaneous layer, filled mostly with fat. This fat serves as insulation as well as fuel storage.